D.C. area rentals?

I'll be in Washington DC for a bit in May visiting relatives, and bringing my bike is not a viable option.

Are there any places you folks know of in DC itself (especially in the Georgetown/Sibley Hospital area) or in the Maryland 'burbs (esp. near Lanham or the US 50/Beltway interchange) to rent decent machines? Road bikes preferred, but I'm not in a position to be real choosy.